This invention relates to a method of and an apparatus for continuous production of seam-welded metal, preferably steel, tubings.
In the art of continuous manufacture of seam-welded steel pipes, a steel strip stock is taken out from a strip coil and subjected to a tube-shaping step and then finally to a seam-welding step. Before seam-welding, and thus during the tube-shaping step, preliminary heating of substantial part of the tubular intermediate product with exception of marginal zones along the opposing longitudinal edges is carried out for releasing residual compressive stresses due to plastic strain induced within said marginal zones in the tube-shaping step, said stresses resulting in disadvantageous formation of what is known as edge wavings or buckling among those skilled in the art, as will be described more fully hereinafter.